Radioactivity involves spontaneous disintegration of unstable atomic nuclei by the emission of subatomic particles including alpha particles (helium ions), beta particles (electrons), and/or neutrons along with the emission of electromagnetic radiation including X-rays or gamma rays. Due to the charged nature of alpha and beta particles, their penetrating ability into matter is limited. However, electromagnetic radiation and especially neutrons can penetrate deeply into matter and thick physical barriers are necessary to provide adequate shielding. Neutron emission and subsequent bombardment is especially damaging to living system and has the unique quality that it can interact with the nucleus of many atoms and destabilize them to cause/promote additional radioactivity.
The release and subsequent interactions of neutrons with another atoms nucleus is the basis of nuclear fission. For example, when a neutron hits a uranium 235 atom, this atom in turn releases about 2.5 neutrons, on average, from the split nuclei. The neutrons released in this manner quickly cause the fission of two more atoms, thereby releasing four or more additional neutrons and thus a self-sustaining series of nuclear fissions, or a chain reaction is initiated resulting results in a sustainable release of nuclear energy. Analogously, when plutonium 239 itself absorbs a neutron, fission can occur, and on the average about 2.8 neutrons are released. Additionally, many atoms can be made radioactive after being hit with a neutron even though they are not capable of sustaining nuclear fission. Instead of releasing neutrons, these atoms release alpha particles, beta particles, and gamma radiation, all of which are highly damaging to living biological systems. Other classes of atoms, called neutron absorbers, can absorb neutrons and yet remain stable; i.e. not radioactive. Thermal neutrons (0 to 500 keV) are absorbed very effectively by specific elements including boron (or B-10 isotope), gadolinium, dysprosium, samarium, cadmium, or europium. Very high energy neutrons (1 to 15 MeV) are absorbed by elements such as zirconium, hafnium, tantalum, indium, hydrogen, or silver.
The power of the atom has been harnessed in several ways including the development of nuclear weapons and in nuclear power plants. Modern nuclear power plants are inherently safe, however, accidents have occurred in the past. In 1979, a nuclear accident occurred in the United States at the Three Mile Island PWR near Harrisburg, Pa. and a small amount of radioactivity escaped from the containment vessel. In 1986, one of four nuclear reactors at Chernobyl exploded and burned for an extended period of time and radioactive material spread over the Ukraine, Scandinavia, and northern Europe.
Since the terrorist attack on Sep. 11, 2001 in the United States, it has become increasingly apparent that the world is an inherently dangerous place. Terrorists, state enemies, criminals, etc. may have at their disposal a wide variety of mass destruction weapons including biological, chemical, and nuclear based weapons. This invention disclosure involves drastically reducing/minimizing the effects of nuclear based/derived weapons by the application of neutron absorber materials/particulates in various forms. Several key scenarios will be listed to give examples of the key embodiments of this invention. Other applications which are not listed but which are variations of this are also covered by this invention.
It has been known since the 1950's that neutron absorbers may be used to moderate the reaction rate in nuclear reactors. Additionally, in the 1990's, it was known that neutron absorbers may have uses in waste packages for the long term storage of nuclear waste. However, there has been no previous knowledge for using neutron absorber materials in the manner identified herein.